The invention relates to a record carrier suitable to be scanned by means of a single scanning head and provided with at least two substantially parallel information layers. Each information layer may comprise information independently of the information contents of other information layers. The information layers may coincide or be separated from each other by a spacer layer. The invention also relates to a scanning device for scanning such a record carrier. During scanning, information can be written, read or erased.
A record carrier of the type described above is known from U.S. Pat. No. 3,855,426. The known record carrier comprises two or more information layers which are separated by spacer layers. An optical scanning device provided with a single scanning head can read one of the information layers by scanning the layer by means of a focused radiation beam from the scanning head. A subjacent or superjacent information layer can be read by means of the same radiation beam by displacing the focus of the radiation beam in a direction perpendicular to the information layer and by positioning it on the desired layer. Due to this mode of serial reading, the collection of information layers in the record carrier can be regarded as a single uninterrupted information area. This is in contrast to a multilayer record carrier which has a scanning head for each information layer. The information areas of the information layers are then read in parallel and should be regarded as separate areas.
There is a need for a multilayer record carrier suitable to be scanned by means of a single scanning head and provided with control information, i.e. information which can be used for reading and/or writing user information in the record carrier. The control information may comprise general data about user information, such as the name of manufacturer of the record carrier, the author of the stored user information, data about encryption, maximum radiation power during writing, reading and/or erasing, and reallocation tables. The control information may also comprise a table of contents indicating the locations in an information area where given parts of the information are stored.
It is an object of the invention to provide a multilayer record carrier which is provided with control information.
In accordance with a first aspect of the invention, the record carrier according to the invention is characterized in that each layer comprises a block of control information having information for scanning said layer.
It is known from the standard for the single-layer record carrier Compact Disc, document IEC 908 to place a block of control information at the start of the information area. When the block of control information is placed on the multilayer record carrier in a similar manner, this will lead to one block of control information at the start of the information area. Consequently, a relatively large block of control information comprising data about all information layers is present at the start of the first information layer. Since the size of the block is dependent on the quantity of stored information, and hence on the number of information layers, the size of the block will also increase as the number of information layers increases. Consequently, the space available for user information on the first information layer will decrease. When information is written in the record carrier, it can thus no longer be assumed that an area per information layer having a given minimum size is available for user information. This is a drawback when planning the way in which the information to be written should be distributed on the different information layers.
The record carrier according to the invention obviates this drawback by providing each information layer with a block of control information having data relating to said layer. For a larger number of information layers, the area of each layer available for user information may remain equal.
A particular embodiment of the record carrier according to the invention is characterized in that the blocks substantially have the same physical location in the plane of the different layers. Consecutive blocks of the information layers can quickly be read one after the other by moving the scanning head to the next information layer over a relatively small distance in a direction perpendicular to the information layers without having to move the scanning head over a relatively large distance in the plane of the information layer.
To be able to scan the user information in the consecutive layers rapidly one after the other, a special embodiment of the record carrier according to the invention is characterized in that user information in one of the layers is sequentially ordered in a given direction in the layer, and in that the user information in another layer is sequentially ordered in the opposite direction. In a disc-shaped record carrier, the user information in a given, first information layer is then recorded, for example from the inner edge to the outer edge and in the next, second information layer from the outer edge to the inner edge. After the information in the first layer has been read, the scanning head only needs to be moved over a relatively small distance to the second information layer so as to read the information in this layer. If the block of control information for the second layer were placed at the customary position, i.e. at the start of the information, then the block would be located at the outer edge of the second information layer, hence not proximate to the block of the first layer. For reading the two blocks one after the other, a relatively large displacement in the plane of the layer would then be required. According to the invention, the block for the second information layer is preferably at the inner edge of the information layer, below or above the block of the first layer. Rapid accessibility of the control information of the different information layers can then be realised.
At least one of the blocks of user information preferably has an indication about the number of information layers in the record carrier. With this information, which is not related to a specific information layer, the scanning device can determine on which information layer the focus spot is positioned.
In a special embodiment of the record carrier according to the invention, at least one of the blocks comprises a sub-block having a global indication about user information stored in the layers. With this information it can be determined in which information layer the information to be read is stored, whereafter the block with the control information on this layer can be read so as to determine the position of the information on the indicated layer.
The invention also relates to a scanning device for scanning a record carrier according to the invention. According to the invention, this device is provided with means for sequentially reading the blocks of control information before reading the user information. After the blocks have been read, information is available for scanning all information layers in the record carrier. For example, the location of all parts of information stored on the record carrier will be known from the tables of contents and the user information to be read can be searched without further reading control information in the blocks.
A second aspect of the invention relates to the distribution of user information on the different information layers. In accordance with this aspect, the record carrier is provided with at least two substantially parallel information layers, in which a first information layer comprises user information in a first format and a second information layer comprises the same user information in a second format. The first format may be a low-density structure and the second format may be a high-density structure. This provides the possibility of reading the same user information by means of different types of playback devices, with each playback device being suitable for playing back one of the formats. In an embodiment of the record carrier according to the invention, this distribution of the user information is combined with the distribution of the user information on the information layers in accordance with the first aspect of the invention. It can thereby be avoided that a relatively large part of an information layer having a low-density structure is occupied by control information related to other information layers.